Impact of Rain on Mileage??

[Larry Riley Jr]

I took my first road trip in the FFH this weekend. It was a quick trip from Atlanta to Fredericksburd, VA (just south of DC) and back. Left on Friday afternoon, returned Saturday afternoon. It's 586 miles each way, and I used eco cruise the entire trip, and kept the speed at 70 MPH. On the way up, I got 41.0 MPG, which is about what I expected. But on the way back, I only got 35.5 MPG. One major difference was the weather: on the way, the weather was pretty much perfect, but on the way back, it pretty rained the entire way back.

 

So my question is, could the rain have made that much of a difference in the mileage? I can't think of any other variables to account for such a big difference other than perhaps I got a bad tank of gas in Virginia?

 

Thanks for any feedback.

[murphy]

Atlanta is about 1000 feet above sea level and Fredricksburg is about 59 feet above sea level.

The first trip was down hill while the second trip was up hill.

Rain will increase the energy required to maintain speed. The faster you go the worse it gets.

[SteveB_TX]

Rain increases the rolling resistance of your tires, so yes, rain will decrease your mpg. I think the primary factor is elevation. Atlanta is approx 1100 ft above sea level. Fredericksburg VA is only approx 60 ft above sea level. :)

 

Edit: Darn you murphy! I was typing while you were posting. ;)

Edited September 22, 2013 by SteveB_TX

[murphy]

Edit: Darn you murphy! I was typing while you were posting. ;)

"Great minds think alike".

:idea:

[Larry Riley Jr]

Thanks! Makes total sense: the route was uphill AND rain had an impact, so it was a double whammy.

[lolder]

The effect of the 1000 ' altitude change over 8 hours is 1/4 hp aiding and retarding. Since it takes about 25 hp to go 70 mph, that's about 1 % so only a 1 mpg difference between coming and going from the altitude change would be expected. The rain and any headwind could easily be the cause. I have seen 10 mpg loss in S. FL. deluges and a 10 mph headwind costs 3 mpg. If vehicles are leaving any spray from a wet road, mpg will be reduced.

Edited September 23, 2013 by lolder

[hybridbear]

Rain increases the hp needed to maintain speed both by increasing rolling resistance when the tires have to plow through water and by increasing resistance when you make contact with the rain drops.

[KingJL]

This past Saturday it rained here most of the day. I took a 50 mi round trip that I normally get right at 46.5 mpg. Between the rain and the wind (there was very little, but it doesn't take much), my mpg dropped to 41 for that 50 mi trip. Just an example of how much effect the weather can have... In a windy area the effects are even more devastating.

Edited September 24, 2013 by KingJL